This research will use genetic analysis to identify and molecularly characterize proteins that are on signal transduction pathways influenced by the Abelson tyrosine kinase (Abl) in Drosophila. Activated Abl kinase is a human oncogene, resulting in both chronic myelogenous leukemia and acute lymphocytic leukemia. As tyrosine kinase signal transduction pathways are often conserved between insects and mammals, insights into Abl kinase signal transduction pathways gained in the Drosophila model system may result in new modes of treatment for these human leukemias. Flies which are homozygous mutant for Abl develop to pupation. New mutations which enhance, or worsen this phenotype, resulting in pre-pupal lethality, have been recovered. In other words animals which are heterozygous mutant for an enhancer mutation and homozygous mutant for Abl die before pupation. As such these new enhancer mutations are in genes which are functionally redundant to the Abl kinase. Two of these new enhancer mutations (M89 and M109) will be mapped to an exact chromosomal location, and cDNAs will be recovered, cloned and sequenced. The expression patterns of these genes will be characterized. New mutant alleles of these genes will be generated and mutant phenotypes will be characterized. cDNAs cloned will be re-introduced into transgenic flies and the rescue of mutant phenotypes will be tested as confirmation that the correct cDNAs have been cloned. A novel genetic screen is also proposed. In a genetic background with sub-optimal Abl tyrosine kinase activity, new mutations will be recovered that alter this background in a kinase-dependent manner. As these mutations depend on Abl kinase activity for their effects, they will likely be in genes which code for proteins which are biochemically associated with Abl's kinase activity, such as direct substrates, kinase regulators or specific phosphatases. These mutations will be mapped to an exact chromosomal location, and cDNAs recovered, cloned and sequenced. The expression patterns of these genes will be characterized. cDNAs cloned will be re-introduced into transgenic flies and rescue of mutant phenotypes will be tested to confirm that the correct cDNAs have been cloned.